Blue Amnesia No.2

The only one of the answers are right - @SpinerGrow. Its defenetly Nitrogen deficiency wich gose farther on 7 week and cause the Iron deficiency as well. All that happend just because your pH is to low for soil substrate. You should rise it at least to 6.2, wich is the lower red line pH in soil before you get a nutrient lock. The soil pH range is 6.5 - 6.2. Advaced growers start with higher pH at veg and gradualy lows it down as it gose in to flowering. My recomendation is to rise the pH to 6.4 and to spray foliar Alg-a-Mic gently on the affected leafs. As well i would make some Urtica(Nettle) tea, wich is the best sourse of Iron. All you need is 250 grams of fresh nettle leafs and 1 litter of RO water. Put the leafs in the water and let it soak for 24 houers in dark with room temperature. Add it to your solution and spray foliar. But Alg-a-Mic will do the job as well. Happy growing Bro!